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Full text of "Alexander von Humboldt"

OF
centre of the globe. These fountains of air often pre-
cipitate the matter they contain, and are frequently
met with in such districts where volcanic traces are
not even visible on the surface of the earth. It has
been before mentioned, that Humboldt explains the
greater richness and luxuriance of antediluvian vege-
tation by the greater quantity of oxygen it received,
and this" rose principally from the oxygen springs, of
which many yet exist (mofettes) and which gave
abundant nourishment to the plants. "What the
plants could not consume was absorbed by the chalk
mountains of the surface, and thus gradually drawn
from the air, which has thereby become respirable
for men and animals. Fluids, slime, and melted
earth, still rise from the centre of the earth, as well as
oxygen and other gases, and the depth of their origin
in our planet can be calculated by their heat. Hum-
boldt connected the places of equal mean tempera-
ture on the surface of the earth by isothermic Iines5
and on the same system it was intended to draw cer-
tain lines showing the equal interior heat, to be called
isogeothermic lines, and these were to be determined
by the temperature of the waters which rise from the
centre of the earth and flow from the tops of the
mountains ; but this method gave very unsatisfactory
results compared to Humboldt's plan, as the tempe-
ratete of these waters is very relative and depends on
many extraneous circumstances. Cold springs only
liave a mean temperature when they, without corning
into contact with the deeper warm springs or the cold
ones from the mountains, have flowed for a consider-
able space in that strata where the permanent tem-
perature of the earth begins, where the warmth of
the air is not influenced by seasons or by day and night.
(This, in the temperate zone, is from forty to sixty
feet ; in the equinoctial regions only one foot below
the surface.) As regards the hot springs, Humboldt
declares, that all those which he and others have dis~
<jovered are situated at a distance from ail volcanos ;
that, therefore, the heat of the interior earth gives